Clear supershell lines before suppressed task

I noticed that when entering the console, I'd often be left with a
supershell line at the bottom of the screen that would eventually get
interlaced with my console commands. This can be eliminated by clearing
the supershell progress before evaluating the task if it is one of the
skip tasks.

main/src/main/scala/sbt/internal/TaskProgress.scala

@@ -57,6 +57,10 @@ private[sbt] final class TaskProgress(log: ManagedLogger)
     ConsoleAppender.setTerminalWidth(JLine.terminal.getWidth)
   }
 
+  override def beforeWork(task: Task[_]): Unit = {
+    super.beforeWork(task)
+    if (containsSkipTasks(Vector(task)) || lastTaskCount.get == 0) report()
+  }
   override def afterReady(task: Task[_]): Unit = ()
 
   override def afterCompleted[A](task: Task[A], result: Result[A]): Unit = ()
@@ -76,10 +80,10 @@ private[sbt] final class TaskProgress(log: ManagedLogger)
     val currentTasks = activeTasks.toVector.filterNot(Def.isDummy)
     val ltc = lastTaskCount.get
     val currentTasksCount = currentTasks.size
-    def report0(): Unit = {
+    def report0(tasks: Vector[Task[_]]): Unit = {
       val event = ProgressEvent(
         "Info",
-        currentTasks
+        tasks
           .map { task =>
             val elapsed = timings.get(task).currentElapsedMicros
             ProgressItem(taskName(task), elapsed)
@@ -92,9 +96,15 @@ private[sbt] final class TaskProgress(log: ManagedLogger)
       import sbt.internal.util.codec.JsonProtocol._
       log.logEvent(Level.Info, event)
     }
-    if (containsSkipTasks(currentTasks)) ()
-    else report0()
-    lastTaskCount.set(currentTasksCount)
+    if (containsSkipTasks(currentTasks)) {
+      if (ltc > 0) {
+        lastTaskCount.set(0)
+        report0(Vector.empty)
+      }
+    } else {
+      lastTaskCount.set(currentTasksCount)
+      report0(currentTasks)
+    }
   }
 
   private[this] def containsSkipTasks(tasks: Vector[Task[_]]): Boolean = {